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A checklist provides an inventory of the species recorded in a region. In its most basic form it will include the accepted scientific name of each species. Most checklists also provide the synonyms of the species which are names that the species was previously or alternatively called, but which under nomenclatural rules are no longer the accepted of the taxon. Synonymy is often complicated, but it is important information that allows literature to be interpreted correctly.

The checklists on this site list the species in each invertebrate group that have been recorded in Ireland since 1800. Species recorded before that, and species which are only known in Ireland from sub-fossil remains are not included

Except for fish, amphibians, reptiles, birds and mammals, all living things that move are invertebrate animals. The invertebrates include single-celled organisms like amoeba, all varieties of worm and shellfish, woodlice and centipedes, the myriad insects, starfish, slugs, spiders, jellyfish, octopus and crabs and many other organisms. Largely immobile animals like sponges, corals, barnacles and sea anemones are invertebrates.

A reasonable estimate of the size of the European Invertebrate fauna is c.100,000 freshwater and terrestrial species. If marine forms (including zoo-plankton) found in Europe's coastal waters were included this total would be closer to c.200,000 species. In the world as a whole, it is estimated that there are only 50,000 species of vertebrate animals.

Many of us find the great variety of invertebrates bewildering and the large number of species offputting. Others feel that because invertebrate animals are small and not much is known about them, they cannot be important. The small size of most invertebrates certainly renders them inconspicuous, so that they are noticed only if they are causing problems. This can understandably lead to the conclusion that invertebrates, apart from those that are good to eat, are generally good for nothing.

Invertebrates specialise in the use of resources which are available only in "small parcels". Thus they frequently live in spaces into which most vertebrates could not squeeze and survive successfully on foodstuffs available in quantities so minute that they are frequently impossible for larger animals even to locate. In this way invertebrates characteristically utilise resources which would otherwise be unused and so be lost to the life system of the planet. Many invertebrates make determined use of food remains discarded as unusable by larger animals. For instance, many invertebrates are dung-feeders, eking out their existence on the energy-rich waste products of the inefficient digestive systems of vertebrate animals and in the process removing what would otherwise represent for humanity a considerable health hazard.

The efficiency with which invertebrates make use of "small parcels" of different resources has led to their being of paramount importance in decomposition processes. Without efficient decomposition much of the sun's energy trapped by plants could not be re-cycled through the ecosystem when plants and animals die. In decomposition processes the particular role of invertebrates is the reduction of dead organic matter to small fragments. The consequences of environmental conditions occurring in which decomposer invertebrates cannot maintain adequate populations can be seen in bogs and fens, where dead plant materials accumulate to great depths as deposits of peat.

In natural woodland, invertebrates are largely responsible for the breakdown into fragments of the wood of dead trees through the biting and chewing action of the jaws of wood-boring insect larvae. In this way, contained nutrients and energy are again made available for re-cycling to growing plants, via the activities of micro-organisms.vertebrate interactions with other animals.

In most healthy agricultural soils, adequate aeration and capacity is maintained principally by the burrowing action of diverse invertebrates. The various earthworms are also important as soil mixers, bringing material from lower soil horizons up to the surface layers by means of their casting activity. It is estimated that there is up to one tonne of invertebrate animals in each hectare of non-desert soil on the planet. All together this would represent a biomass of 1.6 thousand million tonnes of soil invertebrates.

One of the more obvious facets of the role of invertebrates is the part they play in the "food web" of terrestrial, freshwater and marine biotopes. At present, attempts are being made to harvest marine plankton to provide a source of food for man's domestic stock. If these attempts meet with success on any scale we are likely to convert the oceans into biological deserts, due to the total dependence of other marine life upon plankton.

Without an adequate supply of invertebrates as food, Europe's reptile and amphibian fauna would be reduced almost to a single genus of tortoise (Testudo}, only plant-feeder. Similarly, all but 10% of the species in Europes bird and fish faunas would be unable to survive without their own particular invertebrate food supply. Among mammals, to name but two examples, both the mighty blue whale (Sibbaldus musculus) and the tiny pygmy shrew (Sorex minutus) depend upon invertebrates as food. Many of the invertebrates preyed upon by vertebrate animals are themselves dependent upon yet other invertebrates as their own food supply. Indeed, 98% of the potentially harmful invertebrates are prevented from becoming problems by other invertebrates that are either predatory or parasitic upon them. This potentiality has been recognised in the development of programmes of "biological control" of pests. For instance, in Southern and Central Europe, ants of the Formica rufa group are employed on a large scale for control of forest pests.

In schools, invertebrates still represent a peripheral topic and it is unusual for a student to recognise that invertebrate animals have any significance beyond including a Pandora's boxload of multivarious pestilence, offset only by the honey-bee as the sole positive element recognisable among them! And even honey-bees sting! It is hardly surprising that frank incredulity is the normal response to any suggestion that invertebrates should be protected and conserved like other forms of wildlife.

The inevitable preoccupation of the universities etc. with disciplines more "fashionable" than systematics has produced a generation of European biologists lacking the expertise to identify invertebrate species. Equally ecological studies and surveys of invertebrates are inhibited by the reluctance of student and researcher alike to embark upon work requiring a taxonomic expertise they may not possess. The result is that sites of international importance for the conservation of invertebrates are in danger of destruction without their importance having been recognised; invertebrate species are being exterminated over wide areas of Europe without prior warning that they have reached "threatened" status; the invertebrate faunas of Europe's nature reserves and national parks remain largely unsurveyed and unknown and the ecological requirements of most invertebrate species remain conjectural. Europe's invertebrates represent most of the biological diversity existing in the continent. There is a dramatic need forthe immediate introduction of programmes aimed at their conservation. Hopefully, this text will help to focus attention on the problems involved and on what is at stake if these problems are not overcome.